The present invention relates generally to water sprinklers of the impact-arm type, and, more particularly, to impact-arm sprinklers for full-circle rather than part-circle watering.
Typically, an impact-arm sprinkler has a hollow sprinkler body for supplying water from a substantially vertical riser pipe to a nozzle which is mounted on the body at an angle of approximately 10 to 30 degrees above the horizontal. The sprinkler body is mounted on a sprinkler mounting bearing, for rotation about a substantially vertical axis, and an impact arm is mounted for rotation with respect to the sprinkler body, about the same vertical axis. A torsional spring urges the impact arm against a stop affixed to the sprinkler body, and, in this position, a deflector spoon on the impact arm is located directly in the stream of water flowing from the nozzle. The impact arm is thereby deflected by the stream of water, and is rotated, compressing the torsional spring. The force of the spring slows and then reverses the rotation of the impact arm, driving it against the stop on the sprinkler body, and thereby applying an impulse of angular acceleration to the body. The impact arm is repeatedly deflected by the stream of water from the nozzle, and continues to oscillate angularly in this manner, applying an impulse of angular acceleration to the sprinkler body on each cycle of its oscillation.
Although the impact arm is usually balanced, in the sense that it has its center of gravity aligned with its axis of rotation, the deflection force applied to the impact arm by the stream of water is necessarily asymmetrical with respect to the axis of rotation. The force of the stream impinging on the deflector spoon has one horizontal component of force tending to rotate the impact arm about its axis, and has in addition a second horizontal component and a vertical component, both acting in the same plane as the axis of rotation, and both having a tendency to induce wear in the bearing surfaces between the impact arm and the sprinkler body. Even the horizontal component which induces rotation of the arm is not a pure torque force, and results in an asymmetrical reaction force at the impact-arm bearing. The problem is further compounded by the transmission of these asymmetrical forces to the sprinkler mounting bearing connecting the sprinkler body to the stationary water supply pipe.
Further asymmetry results from nozzle reaction forces on the sprinkler body. Flow of water through the nozzle, quite apart from the action of the impact arm, produces vertical and horizontal components of a reaction force, both acting in the vertical plane through the nozzle and its axis of rotation. Again, these asymmetrical forces result in sometimes rapid wear of the bearing surfaces of the bearing on which the sprinkler body is mounted. Moreover, water used for irrigation often contains abrasive silt and sand that can accelerate the wear of both the sprinkler mounting bearing and the impact-arm bearing.
In certain applications, it is desirable to place an irrigation sprinkler at the top of a very tall riser, as for example, when irrigating a fruit crop, such as citrus trees or when used for frost protection. Further, quite frequently such sprinklers are disposed on a relatively long riser which projects downwardly from a supply conduit, such as when used with some center pivot type irrigation systems. It will be appreciated that any non-axial forces generated by a sprinkler disposed on the end of a relatively long riser can result in undesirable vibration and fatigue problems in the riser and its supporting water supply conduit.
Another disadvantage of prior art impact-arm sprinklers is that, when such sprinklers are mounted on sloping ground with the axis of rotation tilted away from the vertical, the speed of rotation is affected by gravitational forces acting on the sprinkler body, and varies cyclically as the sprinkler rotates. Accordingly, there has long been a need in the field of impact-arm sprinklers, for a sprinkler assembly which balances the nozzle reaction forces and impact arm acceleration forces, thereby reducing wear in the bearings of the assembly, and which may be used on sloping terrain without variations in the speed of rotation. The present invention fulfills these needs.